OFFSET
1,1
COMMENTS
(a(n)) is the unique fixed point of the morphism 2->233, 3->2333 (immediate from its definition). - Michel Dekking, Feb 21 2017
REFERENCES
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
LINKS
Reinhard Zumkeller, Table of n, a(n) for n = 1..1000
Bryce Emerson Blackham, Subtraction Games: Range and Strict Periodicity, Master's thesis, 2018.
The Fifty-Fourth William Lowell Putnam Mathematical Competition, Problem A-6, Amer. Math. Monthly, 101 (1994), 727-728.
The Fifty-Fourth William Lowell Putnam Mathematical Competition, Problem A-6, Math. Mag., 67 (No. 2, 1994), 157-158.
FORMULA
a(n) = floor( n*(1+sqrt(3)) ) - floor( (n-1)*(1+sqrt(3)) ).
a(n) = f(n,2,2,2) with f(n,b,c,i) = if n=1 then b else (if c=0 then f(n-1,2,a(i),i+1) else f(n-1,3,c-1,i)). - Reinhard Zumkeller, May 25 2009
MATHEMATICA
f[n_, b_, c_, i_] := f[n, b, c, i] = If[n == 1, b, If[c == 0 , f[n-1, 2, a[i], i+1], f[n-1, 3, c-1, i]]]; a[n_] := f[n, 2, 2, 2]; Table[a[n], {n, 1, 100}] (* Jean-François Alcover, Oct 15 2013, after Reinhard Zumkeller *)
Table[Floor[n (1 + Sqrt@ 3)] - Floor[(n - 1) (1 + Sqrt@ 3)], {n, 120}] (* Michael De Vlieger, Oct 08 2016 *)
t = {2}; Table[If[t[[i]] == 2, AppendTo[t, #] & /@ {3, 3, 2}, AppendTo[t, #] & /@ {3, 3, 3, 2}], {i, 20}]; t (* Horst H. Manninger, Jan 11 2024 *)
PROG
(Haskell)
a007538 n = f n 2 2 2 where
f 1 b _ _ = b
f n b 0 i = f (n - 1) 2 (a007538 i) (i + 1)
f n b c i = f (n - 1) 3 (c - 1) i
-- Reinhard Zumkeller, Feb 14 2012
CROSSREFS
KEYWORD
nonn,easy,nice
AUTHOR
STATUS
approved